M. ribis, Linn, (red-currant aphis), on Ribes rubrum is dimorphic in respect of certain features of the antenna and of abdominal and wing dimensions.
The nature of the food, whether healthy or blistered by the attack of the fundatrix, seems to be the determining factor of this dimorphism.
The form from healthy leaves is probably identical with M. whitei, Theobald, and M. dispar, Patch.
M. ribis is migratory, and in summer colonises certain Labiatæ and other weeds; but this migration is not obligatory, and the entire life-cycle may be passed on currant.
On its summer host plant this species has been previously described as Phorodon galeopsidis, Kaltenbach.
There is a decline in fertility in the later part of the summer among the forms remaining on currant.
This is caused by a lower birth-rate, and not by the shortening of the life of the parent.
This decline, together with the attacks of predaceous and parasitic enemies, accounts for the frequent disappearance of the species from currant in August and September.
Both sexual forms may be produced, and eggs may be laid, on either host plant. Males transferred from Labiatæ to Ribes can fertilise the females on the latter plant.